The present invention relates generally to pens with replaceable roller ball cartridges.
In general roller ball pens have a pen body into which a replaceable roller ball cartridge is held in place such that a user may write with the pen. The roller ball cartridge has a writing tip and a butt end. Usually the pen body has two pieces detachably held together by threads, for example. In order to replace the roller ball cartridge the two pieces are separated and the spent roller ball cartridge is removed and a replacement roller ball cartridge is inserted into one of the two pieces and the other piece is attached back into place. In some cases a spring or other biasing element abuts the butt end of the roller ball cartridge at one end and the inside of the body at the other end, such that the spring biases the writing tip out of the pen body. The spring or biasing element also provides a certain feel to the user, because, depending on the biasing force, the roller ball cartridge will have a certain recoil within the body while the user is writing with the pen. The prior art pens only provide one tension, which is set by design, and a user must be satisfied with the feel of the particular pen chosen. Therefore, there is a need in the art for a roller ball pen for which the user can set the biasing force to meet the user""s particular needs.
A preferred embodiment of roller ball pen includes a pen body with distal and proximal ends, a roller ball cartridge inserted into the pen body (with the writing end extending at least partially out of the distal end of the pen body), a cap detachably attached to the proximal end of the pen body, a drive rod rotatably fixed to the cap, a control member, such as a nut, and a biasing element (preferably a spring) attached to the nut and abutting the butt end of the roller ball cartridge. Preferably, the control member, such as a nut, is slidingly disposed within the cap such that it may move distally or proximally, but may not substantially rotate therein. The drive rod extends at least partially into the cap and is rotatably fixed thereto such that it may not substantially move distally or proximally. The distal end of the drive rod engages the control member, such as a nut, so that rotation of the drive rod will move the nut distally or proximally, thereby changing the biasing force of the spring against the roller ball cartridge. Preferably there is a drive knob fixed to the proximal end of the drive rod and the drive knob is rotatable to rotate the drive rod.